Combination adjuster and reset mechanism



June 25, 1963 J. A. TANKERSLEY ETAL COMBINATION ADJUSTER AND MECHANISMFiled March 21, 1956 ".ITEA

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June 25. 1963 J. A. TANKERSLEY ETAL 3,095,064

COMBINATION ADJUSTER AND RESET MECHNISM Filed March'21, 1956 2Sheets-Sheet 2 /4c ya 54C 46.: 4 5? .g .//JCc 6 y 20c /Zc ,Mc 72C IIN.lllll .4T TDP/VE),

United States Patent O 3,095,064 COMBINATION ADJUSTER AND RESETMECHANISM James A. Tankersley and Paul A. Driscoll, South Bend,

Ind.; said Tankersley assignor to The Bendix Corporation, a corporationof Delaware Filed Mar. 21, 1956, Ser. No. 572,855 9 Claims. (Cl. 18S-72) This invention relates to a device which automatically `adjusts adisk type brake and also resets the brake to a determined clearance ifthe brake clearance is lost owing to overadjustment which wouldotherwise cause dragging of the brake.

It often happens that an automatic adjuster overadjusts the brake sothat the brake clearances are reduced. When this occurs, the brakes canbecome locked or set in applied position and if the vehicle is movingwith the brakes in this condition, there will result considerable dragand overheating of the brake. One of the reasons for overadjustment inbrakes is `that: the adjuster mechanism operates during a brakeapplication while the brake parts are in a temporarily existing state ofthermal and mechanical distortion. The adjuster functions with the brakeparts in this condition of distortion and thus when the brakes arereleased, and the brake parts return to their original shape, then theadjustment operation has produced an inaccurate clearance. Because ofthe tendency for overadjustment, l have found it desii-able to makeprovision for resetting the brakes following a brake application, inorder to 1re-establish a brake clearance.

This resetting operation will take place by merely pushing on the brakepedal. Once the adjuster has reset the brake, this will relieve anydragging condition or locked condition of the brake.

One of the difficulties of combining a reset function with the automaticadjuster, is a partial loss of the effective piston area which appliesthe brake. It is an object of this invention to provide a constructionwhich will operate in conjunction with a fluid motor, to both adjust andreset the brake, and yet enable full utilization of the piston area forapplying the brake.

Another object of the invention is to obtain an adjuster and resetdevice which is of reduced length so that it can be readily fitted inthe carrier plate of a brake. It is well known that space limitationsare highly important in certain types of brakes (for example, aircraftbrakes) and it will be therefore appreciated that this feature is ofconsiderable importance.

Other features and objects of the invention will become apparent as thedescription develops, with reference to ythe accompanying drawings,wherein a plurality of embodiments of the invention are described by wayof example.

In the drawings:

FIGURE 1 shows the adjuster and reset device in a uid motor actuator fora brake, parts of the brake being shown in fragmentary section;

FIGURE 2 is a modification of the device shown in FIGURE 1, showing adilerent location for the Huid sealing members; and

FIGURES 3, 4, 5 and 6 are further embodiments of the invention, each ofthese gures being detail section views of the device. All parts of thebrake in FIGURES 2-6 are removed except the carrier of the brake.

For a typical disk type brake with which the present invention may beused, see application Serial No. 144,943, filed February 18, 1950, nowabandoned in favor of continuation application Serial No. 577,612, nowU.S. Patent 2,885,033.

Referring rst to the embodiment shown in FIGURE l,

3,095,064 Patented June 25, 1963 ICC the device will be described inconjunction with a disk type brake in which relatively rotatable andnonrotatablc members are clamped together for frictional engagement. Itwill be understood that the device may be used with other types ofbrakes and may also be used for clutches or other wearable devices inwhich it is desired to vary the relative position of membersresponsively to wear.

A Huid motor 10 is mounted in a carrier plate 12 which serves las ahousing for the fluid motor. A number of fluid motors are spacedcircumferentially around the carrier. Not all of the iluid motors needbe equipped with the invention. For purposes of explanation, theselected Huid motor is provided with the invention, The fluid motorincludes a pressure responsive piston 14 which is slidable in cylinderbore 16 and a sealing plug 18 that is threadedly received in the carrier12. Between the pistou and the plug is a liuid chamber 20 whereinpressure developed to displace the piston 14 toward the left `and thusactuate the brake. The piston 14 is engageable with a pressure plate 22which is circumferentially fixed. The pressure plate 22 is splined to afixed part of the vehicle so that rotative movement is prevented, butaxial movement is permitted. The piston 14 forces the pressure plate 22leftwardly, into engagement with a rotor 24 which turns either with thewheel or some other rotatable part of the vehicle. Additional plates,alternately rotors and stators, may be stacked adjacently to thepressure plate in the usual manner.

Piston 14 has a number of stepped bores 21, 23 and 2S which accomodatethe automatic adjuster and reset device designated generally byreference numeral 26.

The adjuster and reset device includes a piston-positioning sleeve 28which is closed at one end 30 and has a snap ring 32 in the opposite endthereof. The sleeve is fixed to the piston by means of a frictionmaterial ring 34 which grips the outer surface of the sleeve. Thefriction created between the ring 34 and the outer surface of the sleeveis determined by a gripping force obtained in whatever degree desired,by a threaded nut 36 which bears against one side of the friction ringthrough a loading spring 38. It will be noted that side 40 of the ringand the mating surface 41 of the piston are inclined so that as thefriction ring 34 is forced toward the right there is a wedging actionwhich forces the ring more tightly `against the outer surface of thesleeve 28. The gripping force between the friction ring 34 and thesleeve 28 is thus controlled by turning down or backing off the nut 36.

An elongated stem 42 is fastened at one end 44 to the plug 18 and has aboss 46 at the other end thereof. The boss 46 has an annular shoulder48. Helical spring 50 is compressed within the sleeve 28 between theshoulder 48 and washer 52 which is held in place by the snap ring 32.Also within the sleeve, is a force-transmitting tubular member 54 whichbears against the washer 52 and is movable into and out of engagementwith the shoulder 48 on the stern through the distance D." It will beseen later in the description that :this distance D between the end ofthe tubular member 54 and the shoulder 48 is the established clearancefor the brake.

The chamber 20 is sealed by means of a number of O-ring seals 56, 58 and60. The fluid pressure developed in chamber 2i) is communicated to theinterior of the sleeve 28, so that none of the effective area of thepiston is diminished by the sleeve 28.

The -ring seal 58 seals the exterior surface of the sleeve so that thefriction ring 34 and the surface whereon git slides is dry and remainsfree of any lubricating effect from the hydraulic Huid.

In operation, fluid pressure is developed Within lthe chamber 20 and theinterior of the sleeve 28, thus moving the piston 14 toward the lett andinto engagement with the pressure plate 22. The pressure plate 22 isforced into frictional engagement with the adjacent relatively rotatablerotor 24 and the stack of interleaved rotors and stators thus arefrictionally compressed. This rictional engagement of the brake partsretards the vehicle.

As the piston 14 moves leftwardly, the sleeve 28 .is also movedtherewith, since they -are `frictionally held together by the ring 34.The sleeve 28 continues to move with the piston until the tubular memberS4, moving through the distance D, engages the shoulder 48 andthereafter the sleeve 2S is held against further leftward movement.

If the brake has worn, so that the clearance of the brake is in excessof the distance D, the piston 14 will continue to move relatively to thesleeve 28 against the frictional resistance of the ring 34. Thismovement of the piston, relatively tto the sleeve, pushes the frictionring 34 along the length ofthe sleeve 28 to a new position thereon.While the sleeve 28 moves with the piston 14, the spring 50 is beingcompressed so that during brake application a part of the applying forceis stored within the device to serve als a retracting `force on thepiston when the applying pressure is released.

When the applying pressure in the chamber 20 is released, the spring `Sacting through the washer 52, will push the sleeve 28 toward the rightuntil it 're-engages the boss 46. This retractile movement of the sleeve28 is equal to the distance D. The friction ring connection 34 with thepiston 14 will also return the piston 14 through a like distance. ltwill be noted that even though the piston 14 might have been displacedalong the length of the sleeve 28 during a brake application, yet theextent of its retraction is equal to the distance D, so that brakeclearance remains constant.

Assume next that the brake has overadjus-ted. In other words, there isless than the clearance D within the brake, and the brakes are partially-or fully applied, even though the brake applying pressure is relieved.The reset operation of the device will now be described:

To relieve this brake dragging condition the brake pedal is depressed.When the brake pedal is depressed, pressure is developed in chamber 20.Since the piston 14 is `already in engagement with the pressure plate22, it is prevented from moving leftwardly. The pressure in the chamberdoes, however, cause a movement of the sleeve 28 relatively to thepiston and in a leftwardly direction through the distance D" untiltubular member 54 engages the shoulder 48 of boss 46. The spring `50 iscompressed by this movement of the sleeve through the distance D. Itwill also be noted that sleeve 28 is moved against the resistance of thefriction ring 34. When the pressure in chamber 20 is relieved, thespring 50 forces the sleeve 28 toward the right through the distance D,also returning the piston 14 through a like distance since the pistonand sleeve are held together through the friction ring 34. By thusinitially moving the sleeve 28 in a leftward direction relatively to thexed piston, it is possible to retract the piston 14 and reset the pistonto its original clearance.

Referrin-g next to the modification in FIGURE 2, it will be shown thatby relocating the O-ring seals 58 and 60, it is possible to immerse thefriction ring 34 in hydraulic tluid in order to obtain a more stablecoefficient of friction between the ring 34 and the piston-positioningsleeve 28. In this construction the O-ring seals 62 and 64 are mountedin the cl amp 36 to expose the friction ring 34 to hydraulic fluid. Thehydraulic fluid permeates the friction ring and coats the engageablesurface of the sleeve 28. The hydraulic fluid acts as a lubricant whichproduces a more constant coetlcient of friction between the ring 34 andthe engageable surface of the sleeve 28. Because of greater consistencyin the coefficient of friction, the operation of the reset and adjustingdevice is less subject to variations. It will be noted that there is acollar 66I between the clamping nut 36 and friction ring 34. The collar66 exerts a compressive force on the friction ring 34.

The operation of the device shown in FIGURE 2 is the same as the deviceshown in FIGURE 1.

Referring next to the embodiment shown in FIGURE 3, parts of the devicecorresponding to those previously described will receive the samereference numeral and the Sub-script LL Piston 14a is slidably mountedin cylinder bore 16a which is formed in carrier 12a. The cylinder boreis sealed at one end by a threaded plugs 18a.

Between the piston 14a and plug 18a there is formed a fluid tightchamber 20a which communicates through a passage (not shown) in thelcarrier 12a with some suitable pressure source.

A loading nut 36a is screwed onto a threaded portion of the piston. Theloading nut is cup-shaped and the turned back portion 67 thereof isengageable with friction ring 34a. Surrounding the friction ring is asplit collar 69 with the inner periphery thereof tapered t-o bias thefriction ring 34a against the outer surface of tubular `member 28a. Thefriction ring grips the tubular member to frictionally hold the piston14a and tubular member 28a together.

At the end of the piston 14a and carried thereby, is a shield ofinsulating material 71 which serves as a heat barrier for the hydraulictluid so that the heat developed by the brakes does not producevaporization of the hydraulic fluid. Within the tubular member 28a thereis a Washer 52a which is held in place by a snap ring 32a. A helicalspring 56a is compressed between shoulder 48a on boss 46a of stem 26aand washer 52a.

The stem 26a is secured to the plug 18a by a nut 44a. The spring 50aholds the end of the sleeve 28a against boss 46a of the stem 26a. Asecond boss 73 having a shoulder 7S is contacted by Washer 52a to holdthe sleeve 23a against movement with the piston 14a. The clearancebetween the washer 52a and shoulder 75 is equal to the distance D whichis the clearance maintained in the brake regardless of wear.

When the chamber 20a is pressurized, the piston 14a is displacedleftwardly, referring to FIGURE 3, to take up brake clearances and applythe brake. As the piston 14a moves, the sleeve 28a is carried therewiththrough the friction ring 34a until the clearance D is taken upwhereupon washer 52a engages shoulder 75 of `boss 73 on the stem to holdsleeve 28a against further movement. lf brake wear necessitates `furtherpiston travel, then the piston continues to move in a protractiledirection with the sleeve 28a fixed and the friction ring 34a is thusdisplaced leftwardly on the sleeve 28a by portion 67 of nut 36a.

When the :applying pressure in chamber 29a is relieved, the Spring 50aforces the sleeve 28a toward the right, through the distance D" until itre-cngages `boss 46a. This movement also carries the piston 14atherewith, through a like distance since the sleeve and piston are hcl-dtogether through the friction ring 34a.

Assume next that the brake is dragging because the clearance D" is lostowing to overadjustme-nt. In this case `the operator pumps the brake todevelop pressure in chamber 20a. The piston 14a is held against movementin a protractile direction since it is already produring brakeapplication. The development pressure does, however, cause the sleeve28a to move leftwardly relative to the piston 14a, through the distanceD against the resistance of sp-ring 50a and friction ring 34a. When thepressure `in chamber 20u is relieved, the sleeve 28a is retractedthrough the distance D" which also carrier the piston 14a therewiththrough the same distance to reestablish the brake clearance.

From the location of O-ring seals 56a, 62a and 64a, it will be notedthat the friction ring 34o and engageable surface of the sleeve 28a areimmersed in hydraulic fluid to obtain a more constant coeiiicient offriction therebetween.

Referring next to the embodiment in FIGURE 4, the piston 1417 isslidably mounted in cylinder bore l6b which is formed in carrier 12b. Afluid chamber 20h is formed in the carrier, this chamber h beingpressurized through communication with a passage 68. Apiston-positioning sleeve 28b is mounted within the piston 14b and iscarried by the piston. At the one end h of the sleeve there is a boss69h having an inclined surface 70. The extreme end of the sleeve isthreaded both interiorly and exteriorly. A clamping nut 36b is receivedon the outer threaded portion and wedges a friction ring 34h between theboss Bub and the inner bore 72 of the piston. The friction ring 34hcreates frictional `force between the piston 14b and the sleeve 28hwhich resists relative movement between these two parts. In thisembodiment, the friction ring 34b is held lixed on thepiston-positioning sleeve 28h, and when relative movement occursVbetween the sleeve 28h and the piston 14b, the friction ring 3411slides on surface 72 of the iston. p The stem 42 in the previousembodiments is replaced by a stud 73 which is threadediy xed in thecarrier. The sleeve 28b has a shoulder 76 which is movable throughdistance D, into and out of engagement with shoulder 74 of stud 73.

Within the sleeve 28h there is a threaded cap 78 having an 0-ring seal80 which seals the interior of the sleeve, and a tension spring 50hwhich is fastened at one end to the cap 78 and at the other end to thestud 73.

O-ring seals 58b and 60h prevent leakage of fluid from the chamber 20hthrough the outer edge of the piston or between the piston 14b and thesleeve 28h. In this embodiment, as well as the others, the combinationadjuster and reset device does not diminish the effective area of thepiston. The entire area of the piston is available to developbrake-applying force.

In operation, brake-applying pressure is developed in chamber 20h todisplace the piston 14b toward the left. Both the piston and the sleeve23h move leftwardly until the brake clearance D is exceeded whereuponshoulder 76 of the sleeve 28b engages shoulder 74 of the stud 73 andfurther movement of the sleeve 28h is prevented. The piston 14h is freeto continue movement against the resistance of friction ring 34b, andmovement of the piston continues until the brake is fully applied.Movement of the piston 14b relatively to the sleeve 28b causes thefriction ring 34h to slide on the surface 72 and thus adjustablypositions the piston toward the left.

While the sleeve 28h moves with the piston 14h through the distance 1),spring 50i; is loaded by elongation to produce a tensioning thereof.This tensioning of the spring 50h serves as a retracting force on thepiston 14b when the brake applying pressure is relieved. When the brakeis released, the spring Sllb pulls the sleeve 28b towards the rightthrough the distance D and the sleeve pulls the piston 14h toward theright through a like distance, since the two are held together byfriction ring 34b. The adjuster retracts the piston by the same distanceD, even though the piston has moved a greater distance on itsprotractile stroke. The distance of the piston from a yfull applyingposition to a release position equals the distance D and thus brakeclearance remains constant.

Assume next that the brake is overadjusted and the clearance D in thebrake is lost so that the piston 14b is bearing against the pressureplate to produce a dragging condition in the brakes. The piston can bereset in the following manner by merely pumping the brake pedal.

When pressure is developed in chamber 2Gb the piston 14b is preventedfrom movement toward the left, since it is already in engagement withthe pressure plate; the applying pressure does, however, cause aprotractile movement of the sleeve 28h toward the left relatively to thepiston 14b until the shoulder 76 engages shoulder 74 on `the stud 73.This movement of the sleeve 28b occurs against the frictional resistanceof the friction ring 34h which slides along the surface 72. While thesleeve 281; is moved through the clearance distance D, the spring 5015is being loaded by tensioning thereof. When the pressure is released,the spring Sb contracts and returns the sleeve 28h through the distance13, and this movement of the sleeve also retracts the piston 141)through the same amount since the sleeve and piston `are held togetherthrough friction ring 34h. In this-marmer, the piston 14!) is retractedthrough the distance D and is thus reset to a position providingclearance in the brake.

Referring next to the embodiment shown in FIGURE 5, parts of the brakecorresponding to those shown in FIGURE 1 have the same reference numeralbut also include the subscript "c. This embodiment of the invention issimilar to the one shown in FIGURE l, in that the return spring iscompressed during protractile movement of the piston, and is similar tothe embodiment shown in FIGURE 3 in that the friction material ring isheld fixed on the sleeve and is slidable on a surface of the piston.

The piston 14C is slidable in cylinder bore 16C and is displacedresponsively to development of pressure in the chamber 20c.Piston-positioning sleeve 28e is located within and is carried by thepiston 14C. The sleeve 28e and piston are held together by a frictionring 34e which is wedged between the two members by a clamping nut 36e.

The fluid in chamber 20c is sealed therein with an 0- ring seal 56e andfluid leakage is prevented through the friction device by O-ring seals62e and 64e` which are located in clamping nut 36e. This arrangement offluid seals is similar to that shown in FIGURE 2. The hydraulic fluidrea-ches the area around the friction -ring 34C; it permeates the ringand covers the slidable surface 72C of the piston. The hydraulic fluidcoating has a lubricating effect which makes a more stable andconsistent coefficient of friction.

A stem 42e is securely held at one end thereof to plug 18e which isscrewed into the carrier 12e, and at the other end of the stern is aboss 46c with a shoulder 48e. Spring 50c is compressed Within the sleeve28e between washer 52e and shoulder 48e. Force-transmitting tubularmember 54e is the same as in the embodiment shown in FIGURE 1.

The operation of this device is substantially the same as that inFIGURE 1. The piston is moved leftwardly relatively to the sleeve 28ewhen the brake clearance is exceeded, and this position is held by meansof the friction ring 34e. During a resetting operation, when the brakeis pumped, the piston is fixed and the sleeve 28C moves leftwardlyrelatively to the piston through the established clearance D so thatwhen the pressure is relieved, the sleeve is returned through a likedistance, also pulling the piston therewith.

Referring next to the embodiment shown in FIGURE ment purposes. Theadjuster and iiuid motor are removed as a unit from the outboard side ofthe brake, so .that the brake doe-s not have to be disassembled in orderto repair or replace the device.

In this embodiment the threaded plug 18d is screwed into the carrier 12dand has The piston 14d is slidable in bore 16d. The piston-positioningsleeve 28d is mounted in the piston 14a' just as in the previousembodiment. A friction ring 34d is wedged between the sleeve and thepiston to frictionally hold these two members together, The location ofthe O-ring seals 58d and 60d prevents access of uid to the friction ring34d. The friction ring thus remains dry, as well as ythe bearing surface72d within the piston. The adjuster and reset operation of thisembodiment is the same as the device shown in FIGURE 4. Whatcharacterizes this embodiment and the embodiment of FIG- URES l, 2, 3and 5 is that the plug 18d can be screwed out of the carrier `andremoved and will carry with it the piston and all the components of theadjuster and reset device, since the plug 18d is fastened to the pistonand sleeve 28d through the stern 42d. This is a very great advantage,since the plug 18d is on the outboard side `of the brake and can bereached without disassembling the rotors and stators which are on theopposite side of the carrier plate.

The embodiment in FIGURE 6 differs from the one shown in FIGURE 1 in thelocation of the O-ring seals, the friction ring `and the surface onwhich the friction ring is slidable during adjustment and resetting ofthe brake.

Although the invention has been described in conjunction with certainselected embodiments, it will be understood by those skilled in the artthat numerous modifications and changes may be made of these exampleswithout departing from the underlying principles of the invention.

We claim:

l. In a brake, the combination of: a tiuid motor carrier, a cylinderbore formed in said carrier wherein a fluid pressure is developed tocause actuation of said brake, a

piston responsive to said fluid pressure slidably received in saidcylinder bore, said piston being centrally apertured to receive `apositioning device, said positioning device including a stem threadedlysecured at one end to said carrier and having a fixed abutment at theother end thereof, a sleeve member received in the piston aperture, afriction ring encircling said sleeve, a threaded member screwed ontosaid piston to bear against said friction ring to develop friction whichimpcdes relative movement between said piston and sleeve, a tubularmember located within said sleeve and operatively secured at one endthereof to said sleeve and engageable `at the other end thereof with thefixed abutment on said stem to prevent further movement of said sleeve,and a spring member which is `compressed between the fixed abutment onsaid stem and a transverse portion of said sleeve, said tubular memberbeing constructed with a length permitting movement of said sleevetogether with said piston, said sleeve movement serving to lcompresssaid spring which then exerts a retractive force on said piston whensaid iiuid pressure is relieved.

2. In a brake, a fluid motor `actuator having a pressureresponsivereciprocable piston element, a `carrier `for said uid motor, anelongated member operatively fixed at one end thereof to said carrier, afirst abutment means constructed along the length of said elongatedmember, reciprocable means limitedly movable with `respect to saidcarrier, a second abutment spaced from said first abutment to permitmovement of said reciprocable means between the limits defined by saidfirst and second abutments, friction means joining said piston andreciprocable means whereby the two are moved together, `a springcornbined with said reciprocable means so `that movement of thereciprocable means in la protractile direction loads said spring, and ahydraulic fluid chamber wherein fluid pressure is developed to moveeither the piston or the reciprocable means in a protractile direction,said spring serving to move the reciprocable means in a retractiledirection through the limited movement permitted thereof and also saidpiston therewith.

3. In a disc brake having a carrier member, a combination adjuster andreset device including `a plug threadedly engaged with said carriermember, a fixed member secured at one end to said plug and at theopposite end having a first stop member formed thereon, a second stopmember secured `to said fixed member intermediate said ends, apressure-responsive element having an inner bore therein, ia positioningmember slidably mounted in said bore, a friction member operativelyconnected to adjacent cooperating surfaces of said pressure-responsiveAit) element and said positioning member whereby relative movementbetween said pressure-responsive element and said positioning member isresisted, a fiuid chamber adjacent one end of said bore, means forpressurizing the fluid in said chamber, said pressure-responsive elementand said positioning member being responsive to said fiuid pressure tocause an application of said disc brake, said positioning member beingprovided with a tianged portion which engages said second stop member tolimit the movement of said positioning member to an established distancewhen the brake is applied, and resilient means operatively connectedbetween said positioning member and said first stop member and loadedb-y said positioning member during protractile movement thereof so `asto develop a force which when the fluid pressure is released acts toretract said positioning member and said pressure-responsive elementthrough said established distance, said pressure-responsive elementbeing adjustably movable in increments relative to said positioningmember in response to said tiuid pressure which overcomes the resistanceof Vsaid friction member subsequent to engagement of said flangedportion with Said second stop member whereby compensation is made forwear of the disc brake.

4. A device for adjusting `and resetting a fluid pressure-responsiveelement, said device including a positioning member having meansconnected to and carried by said pressure-responsive element, saidpositioning member including means responsive to said fiuid pressure,said `connection means including yieldable means for resisting relativemotion between said positioning member and said pressure-responsiveelement, a fixed stop member positioned in said pressure-responsiveelement and extending outside thercof for connection to a stationaryclement, sai-d positioning member being movable through an establisheddistance into operative engagement with said fixed stop during theprotractile stroke of said positioning member and saidpressure-responsive element, and resilient means operatively connectedto said fixed stop and said positioning member and loaded by saidpositioning member during protractile movement thereof so as to developa force which acts to retract said positioniiig member and saidpressure-responsive element through said established distance, saidpositioning member being movable in a protractile direction relative tosaid pressure-responsive element in response to said fluid pressurewhich overcomes the resistance of said yieldable means when saidpressure-responsive element is encrgized to a fixed position at one endof its range of travel.

5. In a brake having a stationary carrier member, a combination adjusterand reset device including a fixed `stop member connected to saidstationary carrier member, a pressure responsive element having an innerbore therein, a positioning member slidably mounted in said bore, afriction member operatively connected to adjacent cooperating surfacesof said pressure responsive element and said positioning member, wherebyrelative movement between said pressure responsive element and saidpositioning member is resisted, a fluid chamber adjacent one end of saidbore, means for pressurizing the fiuid in said chamber, said pressureresponsive element and said positioning member being responsive to saidfluid pressure to cause an iapplication of said brake, said positioningmember being provided with a flanged portion which engages said fixedstop member to limit the movement of said positioning member to anestablished distance when the brake is applied, `a spring connected atone end to said positioning member and at the opposite end to said fixedstop member and loaded in tension by said positioning member duringprotractile movement thereof so `as to develop a force which when thefiuid pressure is released acts to retract said positioning member andsaid pressure-responsive element through said established distance, saidpressure-responsive element being adjustably movable 9 4 in incrementsrelative to said positioning member in response to said fluid pressurewhich overcomes the resistance of said friction member subsequent toengagement of said flanged portion with said fixed stop member wherebycompensation is made for wear of 'the brake, said positioning memberalso being adjustably movable in increments relative to saidpressure-responsive element in response `to said iiuid pressure whichovercomes the frictional resistance of said friction member subsequentto an application of the brake by Said pressure-responsive elementbefore said fixed stop member is engaged by said flanged portionwhereupon said positioning member is actuated in a protractile directionto cause said flanged portion to engage said fixed stop member tothereby reestablish said established distance.

6. In braking mechanism having braking elements mounted for relativemovements tinto and out of engagement, power means for lactuating saidelements, comprising: a cylinder; a main piston reciprocable in saidcylinder; a fixed member extending axially of said main piston; anauxiliary piston Within the main piston surrounding thc fixed member andbeing supported for irelative `axial movement between spaced limits withrespect to the fixed member; spring means acting to bias said auxiliarypiston towards one limit of its movement; and 4a friction connectionbetween said main piston and said auxiliary piston normally connectingsaid pistons for unitary movement, but enabling relative movementthereof when `the frictional force of said connection is eX- ceeded.

7. In braking mechanism having braking elements mounted for relativemovements tin-to and out of engagement, power means for actuating saidelements, comprising: a cylinder; a main piston reciprocable in saidcylinde-r; a fixed member extending axially of said main piston; anauxiliary piston within the main piston surrounding the xed member andbeing supported for relative axial movement between spaced limits withrespect to `the xed member; Spring means `acting to bias said auxiliarypiston towards one limit of its movement; and a friction connectionbetween said main piston yand said auxiliary piston normally connectingsaid pistons for unitary movement, but enabling relative movementthereof when the frictional force of said connection is exceeded, saidfriction connection comprising la grip ring carrie-d by said main pistonand having engagement with said auxiliary piston; and means carried bysaid main piston for adjustably regulating the frictional gripping forceof said grip ring with respect to said `auxiliary piston.

8. In braking mechanism having braking elements mounted for relativemovements into and out of engagement, power means for actuating saidelements comprising: a cylinder; a main piston reciprocable in saidcylinder; a fixed member extending axially of said main piston; anauxiliary piston within the main piston surrounding the fixed member andbeing supported for relative axial movement between spaced limits withrespect to `the fixed member; spring means acting to bias said auxiliarypist-on towards one limit of its movement; and a friction connectionbetween said main piston and said auxiliary piston normally connectingsaid piston for unitary movement, but enabling relative movement thereofwhen the frictional force of said connection is exceeded, said frictionconnection comprising an expansion ring carried by said auxiliary pistonand having engagement with said main piston; and means carried by saidauxiliary piston for adiustably regulating `the frictional force of saidexpansio-n ring with respect to said main piston.

9. In braking mechanism having braking elements mounted for relativemovements into and out of engagement, power means for actuating saidelements, comprising: a cylinder; a main piston reciprocable in saidcylinder; a fixed member extending axially of said main piston; anauxiliary piston within the main piston surrounding the fixed member andbeing supported for relative axial movement between spaced limits withrespect to the fixed member; spring means acting tto bias said auxiliarypiston towards one limit of its movement; and a friction connectionbetween said main piston and said auxiliary piston normally connectingsaid pistons for unitary movement, but enabling relative movementthereof when the frictional force of said connection is exceeded, saidfriction connection comprising an expansion ring carried by saidauxiliary piston adapted to engage said main piston with a predeterminedpressure and frictionally oppose relative movement between the mainpiston and vthe auxiliary piston.

References Cited in the tile of this patent UNITED STATES PATENTS2,392,970 Bricker Ian. l5, 1946 2,496,699 Clark Feb. 7, 1950 2,568,858Kovac Sept. 25, 1951 2,644,549 Cagle July 7, 1953 2,746,254 Lucien May22, i956

1. IN A BRAKE, THE COMBINATION OF: A FLUID MOTOR CARRIER, A CYLINDERBORE FORMED IN SAID CARRIER WHEREIN A FLUID PRESSURE IS DEVELOPED TOCAUSE ACTUATION OF SAID BRAKE, A PISTON RESPONSIVE TO SAID FLUIDPRESSURE SLIDABLY RECEIVED IN SAID CYLINDER BORE, SAID PISTON BEINGCENTRALLY APERTURED TO RECEIVE A POSITIONING DEVICE, SAID POSITIONINGDEVICE INCLUDING A STEM THREADEDLY SECURED AT ONE END TO SAID CARRIERAND HAVING A FIXED ABUTMENT AT THE OTHER END THEREOF, A SLEEVE MEMBERRECEIVED IN THE PISTON APERTURE, A FRICTION RING ENCIRCLING SAID SLEEVE,A THREADED MEMBER SCREWED ONTO SAID PISTON TO BEAR AGAINST SAID FRICTIONRING TO DEVELOP FRICTION WHICH IMPEDES RELATIVE MOVEMENT BETWEEN SAIDPISTON AND SLEEVE, A TUBULAR MEMBER LOCATED WITHIN SAID SLEEVE ANDOPERATIVELY SECURED AT ONE END THEREOF TO SAID SLEEVE AND ENGAGEABLE ATTHE OTHER END THEREOF WITH THE FIXED ABUTMENT ON SAID STEM TO PREVENTFURTHER MOVEMENT OF SAID SLEEVE, AND A SPRING MEMBER WHICH IS COMPRESSEDBETWEEN THE FIXED ABUTMENT ON SAID STEM AND A TRANSVERSE PORTION OF SAIDSLEEVE, SAID TUBULAR MEMBER BEING CONSTRUCTED WITH A LENGTH PERMITTINGMOVEMENT OF SAID SLEEVE TOGETHER WITH SAID PISTON, SAID SLEEVE MOVEMENTSERVING TO COMPRESS SAID SPRING WHICH THEN EXERTS A RETRACTIVE FORCE ONSAID PISTON WHEN SAID FLUID PRESSURE IS RELIEVED.